盾构穿越砂卵石地层地表沉降特征细宏观分析

Meso-macro analysis of surface settlement characteristics during shield tunneling in sandy cobble ground

以成都砂卵石地层中地铁1号线的土压平衡盾构掘进施工为研究背景,采用室内试验、PFC2D二维颗粒流程序和Plaxis 3D有限元软件对盾构穿越砂卵石地层地表沉降特征进行了细宏观数值模拟,揭示了土压盾构穿越砂卵石地层的失稳机制和沉降规律,并结合实际施工参数和实测地表沉降数据进行了对比分析,获得了土压盾构在砂卵石地层中掘进引起的地表横向沉降槽和纵向沉降槽曲线,分析了不同大小的开挖面土仓压力和盾尾注浆压力对地表沉降的影响,给出了砂卵石地层开挖面土仓压力的建议值和盾尾注浆压力参数的合理取值范围。细宏观分析表明,与注浆压力相比较,土仓压力对地表最大沉降曲线的形状影响较小;但必须关注土仓压力的变化,在砂卵石地层中由于土拱效应对开挖面稳定性影响较大,甚至发生突然坍塌破坏。

The process of shield tunneling at Chengdu Metro Line 1 in sandy cobble ground is simulated in meso-scale and marcoscale by laboratory experiment and using particle flow code in 2D （PFC^2D） and finite element software of Plaxis 3D, respectively. The settlement character and failure mechanism driving by earth pressure balance shield （EPBS） in sandy cobble ground are revealed. Based on the comparison of the estimated values from meso and macro simulation results with the in-situ soil settlements and construction parameters, the surface settlement trough and subsidence patterns are approached. The influence of the chamber pressure at the tunnel face and the grouting pressure at the tail gap on the ground surface subsidence are analyzed; and the suitable values for the chamber pressure at the tunnel face and the grouting pressure at the tail gap are suggested. Compared to the grouting pressure, chamber pressure has relatively smaller effect on both the shape of the curve and the maximum surface settlement based on the analysis results. However, much attention should be paid to the chamber pressure, which may have greatly influence on the stability of the tunnel face and result in abruptly collapse in sandy cobble ground due to the effect of arching.